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V Bloch

Publications and source records attributed to V Bloch.

At least 19 recordsLinked to original sources
PubMed1992

Responses of hippocampal cells can be conditioned during paradoxical sleep.

To test the hypothesis that new associations can be acquired during sleep, we developed a conditioning paradigm in which both conditioned (CS) and unconditioned (US) stimuli were non-awakening intra-cerebral stimulations. The CS was a stimulation of the Medical Geniculate body and the US a stimulation of the Central Grey. An increase in hippocampal multiunit activity to CS was taken as the conditioned response. CS-US pairings were presented across 14 sessions, with 15 trials per session and a 24-h inter-session interval. Three groups were studied: in a group the CS-US pairings were given during the awake state (group W), and in two groups pairings were presented during sleep, either slow-wave sleep (group SWS) or paradoxical sleep (group PS). In the last group, to test the possibility of transfer to the awake state of the hippocampal response acquired in PS, the CS alone were presented interspersed with periods of wakefulness. Results showed that, before pairing, CS presentation induced no change in hippocampal multiunit activity in the three groups. After pairing, no hippocampal response to CS presentation occurred in SWS. In contrast, in the W group and in the PS group, a marked increase in hippocampal activity appeared to CS. The hippocampal response in the PS group developed progressively across sessions; it occurred only two sessions later than in the W group. Moreover, when the CS-evoked response reached the asymptotic level in PS, the presentation of CS alone in awake animals elicited the hippocampal response. These results suggest that a cellular conditioning can be established during PS and that the cellular conditioned response developed in PS can be transferred to the awake state.

Animals↗
PubMed1989

Linear relation between the magnitude of long-term potentiation in the dentate gyrus and associative learning in the rat. A demonstration using commissural inhibition and local infusion of an N-methyl-D-aspartate receptor antagonist.

Field potentials were recorded in the dentate gyrus of freely-moving rats in a classical conditioning paradigm in which high-frequency stimulation of the perforant path served as a conditioned stimulus. Paired or unpaired perforant path stimulus-footshock presentations were given to animals engaged in a previously acquired food-motivated lever-pressing task. Conditioned suppression of lever-pressing was the behavioural measure of conditioning. Perforant path stimulus trains at an intensity above spike threshold induced long-term potentiation of synaptic transmission in the dentate gyrus. In this condition, animals learned the perforant path stimulus-shock association. Three strategies were employed to block the induction or reduce the magnitude of long-term potentiation induced by the conditioned stimulus: (1) reduction of the intensity of the stimulus below the spike threshold resulted in no long-term potentiation and a failure by the animals to learn the perforant path stimulus-shock association; (2) inhibitory modulation of long-term potentiation by high-frequency activation of commissural input to the dentate gyrus resulted in learning deficits; (3) chronic infusion of DL-2-amino-5-phosphonovalerate, a selective antagonist of the N-methyl-D-aspartate subtype of glutamate receptor, blocked the induction of long-term potentiation and prevented associative learning. A highly significant linear relation emerged from a correlational analysis between the magnitude of the change in synaptic efficacy at the activated synapses and the amount the animals learned about the perforant path stimulus-shock association. The results presented in this paper are consistent with the hypothesis that associative learning depends on the development of lasting changes in synaptic function. We propose that the activation of N-methyl-D-aspartate receptors in the dentate gyrus is involved in this process and that the more change in synaptic efficacy is produced in the activated network, the more the animals learn.

2-Amino-5-phosphonovalerate↗
PubMed1989

Improvement of learning by mesencephalic reticular stimulation during postlearning paradoxical sleep.

Evidences have been given which suggest that a newly formed memory trace is processed during paradoxical sleep (PS) following learning. The present experiments were aimed at testing the hypothesis that during postlearning PS the new memory trace is in a similar state as immediately after acquisition. For this purpose, a mild electrical stimulation of the mesencephalic reticular formation (MRF)--known to enhance retention performance when delivered just after learning--was administered during postlearning PS phases. Wistar rats were trained to run in a six-unit spatial discrimination maze for food reward. After each daily trial, extradural cortical electrodes (ECoG) activity was monitored polygraphically for 4 h. Half of the animals received nonawakening MRF stimulations during the first six phases of PS. Control rats received no stimulation. The learning results showed a marked improvement in performance, in terms of error number reduction, in the stimulated group. Results of a second experiment confirmed the facilitative effect of MRF stimulations given during postlearning PS. Moreover, they emphasized the specific role of PS, by showing that the same stimulations were ineffective when delivered, at the same time intervals after training, during six periods of waking or six periods of slow-wave sleep. These results lend support to the idea of a reactivation of the new memory trace during PS. They suggest that dynamic processes, similar to those immediately following acquisition or exposure to a reactivating treatment (i.e., a reminder), take place during postlearning PS.

Animals↗
PubMed1985

Enhancement of long-term potentiation in the rat dentate gyrus by post-trial stimulation of the reticular formation.

The possibility that post-trial stimulation of the mesencephalic reticular formation (m.r.f.) may modulate long-term potentiation (l.t.p.) at the perforant path to dentate granule cell synapses was studied in freely moving rats. Extracellular potentials evoked in the dentate gyrus by test pulses to the perforant path were recorded before and at various delays after a series of high-frequency stimulus trains to the perforant path (ten trains of eight pulses at 400 Hz, delivered at 5 min intervals). We have compared the magnitude and duration of l.t.p. of the population spike in this control condition with that observed when a low-intensity m.r.f. stimulation was delivered 10 s after each train to the perforant path. Post-event m.r.f. stimulation enhanced the amount of l.t.p. induced by the series of high-frequency stimulus trains and prolonged its duration for several days. The size of the population spike was unaffected by repeated m.r.f. stimulation in the absence of perforant path high-frequency stimulation, or when this failed to induce significant l.t.p. The temporal gradient of efficacy of m.r.f. stimulation was investigated. M.r.f. stimulation delivered 10 s after a single high-frequency stimulation of perforant path fibres resulted in an enhanced l.t.p. of both the population excitatory post-synaptic potential (e.p.s.p.) and population spike. L.t.p. was unaffected by m.r.f. stimulation given either before, or 120 s after perforant path high-frequency stimulation. These results show that low-intensity m.r.f. stimulation enhances lasting changes in synaptic function in the dentate gyrus when delivered during a critical period following high-frequency activation of perforant path fibres. These results are discussed in the light of our previous findings on the effects of post-event m.r.f. stimulation on memory and on the development of associative changes in hippocampal multiunit activity during conditioning. It is hypothesized that l.t.p.-like mechanisms may be involved in the stabilization of neural networks by experience and that this process might be reinforced by diffuse m.r.f. activation.

Action Potentials↗
PubMed1984

Facilitation of generalization performances in spatial learning problems by posttrial stimulation of the mesencephalic reticular formation.

The effects of low posttrial stimulation of the mesenphalic reticular formation (MRF) on spatial learning problems were studied in two consecutive stages. First, the performances of stimulated (S) and no-stimulated (NS) subjects were assessed in a reconvergent three-arm maze. Secondly, the same animals were tested in a generalization paradigm, since they had to solve a similar task in a radial four-arm maze, each group being divided into newly stimulated (S-S, NS-S) or no-stimulated (S-NS, NS-NS) subjects. In the first experiment, no differences were found between the acquisition processes of groups S and NS. Conversely, in the second experiment, previously stimulated animals (S-S and S-NS) showed better generalization of the experimental rule. The results are discussed in terms of preservation of the neural activity after the early MRF stimulation. From a functional point of view, our data indicate that an enhancement of the neural activity during acquisition facilitates not only a high accessibility of memories concerning the experimental rule in a subsequent similar situation but also the capability to apply a previously elaborated response system in a more complex situation.

Animals↗
PubMed1983

Post-trial reticular facilitation of associative changes in multiunit activity; comparison between dentate gyrus and entorhinal cortex.

Multiunit activity recorded in both the dentate gyrus and the entorhinal cortex during classical conditioning was studied in freely moving rats receiving a mild post-trial stimulation of the mesencephalic reticular formation. Dentate multiunit activity progressively increased in response to an auditory signal (conditioned stimulus) after pairing the signal with a footshock (unconditioned stimulus). No such increase was seen in the entorhinal cortex of the same animals during conditioning. Post-trial reticular stimulation facilitated the development of associative changes in dentate multiunit activity, while having no effect in the entorhinal cortex. The results were interpreted as indicating a possible specificity of action of post-trial reticular stimulation on learning-induced plasticity and are discussed in relation to the concept of neural perseverance in memory consolidation.

Animals↗
PubMed1981

Conditioning of hippocampal cells: its acceleration and long-term facilitation by post-trial reticular stimulation.

Neuronal activity, recorded in the dorsal hippocampus (CA3) during classical conditioning, was studied in rats receiving mild post-trial stimulation of the mesencephalic reticular formation. Hippocampal multi-unit activity increased in response to an auditory signal (conditioned stimulus) after pairing of the signal with a footshock (unconditioned stimulus), while the auditory signal alone, presented before conditioning, did not change the rate of hippocampal cell discharges. Trial-by-trial analysis of hippocampal multi-unit responses to the conditioned stimulus, both during acquisition and during a test of long-term retention, indicated that post-trial mesencephalic reticular stimulation hastened the onset of cellular conditioning and facilitated conversion to long-term storage. A study of evoked potentials recorded in the hippocampal formation to stimulation of the perforant path in awake rats, suggested that these effects could be mediated through a modulation of synaptic efficiency within hippocampal neuronal networks. These data are discussed in relation to the concept of neural perseveration in memory consolidation.

Animals↗